Kidney stones, and also naturally-occurring stones in the bladder and the ureter can be exquisitely painful, and often require surgical relief. Excision or destruction of stones in the bladder and sometimes in the ureter can be relatively easily accomplished, but removal of stones from the kidney is a major procedure.
Removal of stones from the kidney is a very serious and traumatic surgical procedure. A large incision is made in the body. The kidney is essentially removed from the body and cut open. The stone or stones are then removed, whereupon the kidney is sutured and returned to the body, with the body then being sutured. Various efforts have been made to destroy or disintegrate kidney stones so that they can be excreted with the urine.
Chemotherapy is available as a non-invasive therapy for uric acid stones. In this therapy, the urine is alkalyzed, and the stone is dissolved over a substantial period of time. This requires detection of the stone before an acute phase is reached.
The next step was the use of ultrasound or an electrohydraulic shock wave produced by discharging a capacitor across a spark gap under water or other suitable liquid. Early efforts required invasion of the body, either through the urethra or through a surgical incision.
Subsequently, efforts have been made for the extracorporeal destruction of kidney stones through the use of a focused shock wave. In U.S. Pat. No. 3,942,531, for example, a reflector is used which is a portion of an ellipsoid. The spark gap is located at the first focus point of the ellipsoid, and the ellipsoid is positioned relative to the body so that the kidney stone or other calculus or concretion is at the second focus point of the ellipsoid. The reflector is filled with water. Discharge of a spark across the gap causes rapid vaporization of a portion of the water, and resultant generation of a shock wave which is focused by the reflector on the kidney stone. The shock wave travels through the water in the ellipsoidal reflector, and through the human tissues to the kidney stone. A repetition of the spark gap shock wave generation over a period of perhaps an hour, is necessary to destroy a kidney stone.
Repeated shock wave generation as just described results in an accumulation of gas within the water in the reflector. It has been found that the best approach to the human body is to have the patient lie on his back with the ellipsoidal reflector below him. This results in collection of gas at the interface between the water in the reflector and the body of the patient This materially reduces energy transfer from the shock wave generator to the human body, and inhibits destruction of a kidney stone.
Simply replacing the water in the reflector has little effect in removing the gas, which tends to remain as an air bubble at the top of the reflector and beneath the diaphragm. This problem is exacerbated by a tendency of the gas to adhere to the underside of a diaphragm.